The present invention relates to a reactor vessel and to a process for preparing a controlled-dosage chlorine dioxide solution.
In particular, the present invention relates to a reactor vessel for household or hospital use and to the corresponding process for the on-site preparation, dosage and correction of chlorine dioxide solutions which have a high-level sanitizing and disinfecting action.
Containers are known, particularly in the field of detergents and disinfectants, which allow to dose the liquid contained therein before using them.
In particular, containers are known which are formed monolithically and have a body in which two chambers are provided which have mutually different volumes: the smaller-volume chamber, meant to be used to measure the liquid to be dispensed, usually has graduations and is placed at a higher level than the larger-volume chamber, which contains the liquid to be dosed. The smaller-volume chamber is furthermore connected to the larger-volume chamber by means of a duct which usually runs vertically and has an inlet arranged proximate to the bottom of the larger-volume chamber and an outlet arranged in a region which is spaced upward from the bottom of the smaller-volume chamber.
In practice, these containers have a single dispensing opening, which is closed by a removable plug and is located in the smaller-volume chamber in order to allow to dispense the product after dosage thereof, which is carried out in the smaller-volume chamber.
With these containers, the liquid to be dosed is placed in the larger-volume chamber and the user, by compressing the container in the region occupied by the larger-volume chamber, causes the intended amount of product to rise from the larger-volume chamber to the smaller-volume chamber until the intended level of product is reached inside the smaller-volume chamber, using the graduations provided in said chamber as a reference.
Precision of the dosage of the product inside the smaller-volume chamber depends on the skill and attention of the user.
Moreover, this kind of containers cannot be used as reactors for preparing controlled-dosage solutions of substances that can release vapors during reaction if said vapors might be noxious or irritant, because the contact between the two substances that must react together occurs in the smaller-volume chamber and this entails removing or in any case loosening the plug that closes the smaller-volume chamber in order to allow the transfer of the substance located in the larger-volume chamber to the smaller-volume chamber.
It is also known that chlorine dioxide is prepared industrially and exclusively in the form of an aqueous solution and that its main use is to render water potable or to disinfect swimming pools or polluted water.
Industrial preparation is performed by feeding a solution of sodium hypochlorite or acid, by means of a pump, into a reactor into which a sodium chlorite solution is fed by means of another pump. Starting from the time of contact, and also thereafter, due to the continuous inflow of the reagents, dioxide gas develops continuously and is fed continuously into a water stream the flow rate whereof is proportional to the amounts of the reagents used to obtain the intended concentration in the water. Chlorine dioxide is highly unstable and this explains why despite being a low-toxicity sterilizing disinfectant it is not commercially available as a concentrated solution to be diluted at the time of use.
In order to obviate instability, attempts have been made to prepare the chlorine dioxide solution at the place of use.
Construction and management of a sufficiently economical small system for obtaining small amounts of chlorine dioxide at the point of use, for example those required to disinfect a private dwelling or a hospital or the sanitary services of a community, have never occurred because the system is expensive owing to the use of safety-type vacuum or pumping devices.
Moreover, their use cannot be entrusted to unskilled persons, as occurs in a household environment, or to people who are rotated continuously, as occurs in a cleaning contractor charged with disinfecting a hospital environment.
It would be indispensable to have devices to avoid the formation of pockets of gas with a concentration of more than 10% by volume (approximately 300 g/m.sup.3), since the gas is unstable and can decompose violently.
Current systems are furthermore bulky and operate continuously in order to introduce dioxide into streams of running water.
Once dissolved in water, the dioxide is not stable for more than two or three days, and then the concentration which continuously decreases does not allow to perform the necessary controlled dosages: this fact prevents the production of the dioxide in a suitable plant, as well as its storage and commercialization.
The above facts explain the need and convenience of setting up the problem in a new way and of bringing the preparation of dioxide to the point of use by means of a mini-reactor and of a safe and simplified method for producing a highly pure solution.
Attempts to produce highly concentrated solutions of chlorine dioxide in pure form have led to the production of solutions with a concentration of ClO.sub.2 no higher than 93% and with rather low purity, owing to the presence of contaminants which are mainly constituted by partially unreacted reagents and intermediates.
Canadian patent no. 959,239 in the name of Callerame discloses a conventional process for producing chlorine dioxide by reacting an alkaline metal or an alkaline-earth metal such as sodium chlorite and an acid. The composition obtained as a result of the acidification of the sodium chlorite does not have the sought disinfectant effectiveness, especially in terms of germicidal rate. In order to compensate for this shortcoming, it is necessary to resort to the use of a high concentration of sodium chlorite and acid, which can lead to toxicity problems, particularly when the composition is used in an enclosed space. The composition obtained by the interaction of sodium chlorite and acid furthermore does not produce an effective solvent environment for products that contain active chlorine, such as chlorine dioxide, chlorous acid and the like.
Inhaling these components can be noxious.
Accordingly, these toxicity problems have forced various limits to the general use of the disinfectant composition.
U.S. Pat. No. 4,084,747 in the name of Alliger discloses a composition which comprises a water-soluble chlorite, such as sodium chlorite, with a solution of lactic acid. This composition has improved disinfectant properties with respect to others that use an acid other than lactic acid, but it is necessary to heat the solution to 50.degree. C. in order to achieve a good disinfectant action.
This limitation, however, entails the drawback that it does not allow practical use of the solution and does not allow to control the formation rate of chlorous acid and therefore to control the chlorine dioxide.
More recently, patent WO 85/04107 in the name of Alcide Corporation discloses a synergistic disinfectant composition which comprises a compound capable of releasing dioxide, an organic acid other than lactic acid, and a polyhydroxylated compound. The use of this composition, however, is mainly aimed at preparing products in gel form for disinfecting human mucous membranes, with particular reference to use in toothpastes.
Even more recently, patent EP 0 581 550 in the name of Yosef was published, claiming a composition which is suitable to release ClO.sub.2 in water; the composition comprises a water-soluble chlorite salt, a proton donor agent, and a chlorine donor agent which act as an oxidizing agent, such as Na/K-DCC, which is suitable to activate the reaction.
It is thus evident that the methods of the prior art entail drawbacks linked to the difficulty of adjusting the development of chlorine dioxide and to the possibility of producing it in amounts suitable for household use in a pure form which is stable and effective from the point of view of germicidal activity. Moreover, most conventional processes do not allow to limit the development of dioxide vapors, which are inherently toxic and certainly irritant for the upper respiratory tract even when inhaled in rather diluted amounts.
Finally, it is noted that the use of certain components (for example Na-DCC, chlorinated derivatives, solvents, etcetera) in the reaction mixtures can be an additional factor which entails a high toxicological and allergologic risk in use, owing to the formation of secondary compounds caused by the chlorinating action of chlorine.